Nonlinear optics and frequency conversion: fiber lasers in IR, VIS and UV

Abstract

Various techniques are described for the efficient non linear conversion of high power fibre laser sources. These include the frequency doubling in periodically poled crystals of polarization preserving high power fibre Raman masteroscillator power fibre amplifier schemes, or the frequency doubling of a high power, narrow line bismuth-doped fibre laser, primarily for visible generation in the region of 589 nm. Above 2 microns where loss in silica based fibres prohibits efficient Raman generation, the use of heavily doped (~75%) GeO₂ fibres has been demonstrated as an efficient and effective all-fibre configuration to extend high power cw operation into the near infra red spectral region. For many applications, high peak power multiple wavelengths are required simultaneously. The integration of pulsed fibre lasers operating around 1 &mgr;m and photonic crystal fibre provides a simple mechanism to achieve this goal. Generally, the upper wavelength limit of supercontinuum generation is restricted by propagation loss and this has a consequential effect of inhibiting short wavelength generation through four wave mixing in the fibre. We have developed a technique employing long lengths of tapered PCFs that allow efficient phase matched four wave mixing to the short wavelength region and permits the generation of spectral power densities as high as 5mW/nmin the uv.